<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<div id="el">
    <button v-on:click="clickHandler">test</button>
    <p>{{ o }}</p>
    <p>{{ dog.name }}</p>
</div>
<script src="../vue.js"></script>
<script>
    let vm = new Vue({
      el: '#el',
      data: {
        o: 'object',
        dog: {}
      },
      methods: {
        clickHandler() {
          // this.dog.name = 'Trump'
          this.$set(this.dog, 'name', 'Trump')
        }
      }
    })
</script>
</body>
</html>